Unmanned helicopters are frequently used for exploration purposes. Such helicopters are often operated from ships. Therefore, UAV helicopters must be easily transportable and light-weight. Furthermore, UAV helicopters should be easy to store on a ship, when not in use. The propulsion of the rotors should thus allow for quick and easy assembly/disassembly of the helicopter, thereby simplifying transportation and storage. Additionally, UAV helicopters should be easy to maintain.
Dismountable helicopters are generally known. For example, a modular airframe and rotor unit is known from GB 2,359,533. The torque compensating rotor in the tail of the helicopter is driven by a thin-walled drive shaft, detachably connected to the main power drive. A belt drive propulsion of the tail rotor is not disclosed.
U.S. Pat. No. 3,029,047 describes a collapsible helicopter which comprises certain pivotable or foldable components. The helicopter may be disassembled and collapsed into a portable and light-weight package for transportation. This type of helicopter is, however, not unmanned and its tail rotor is driven by a drive shaft. A belt drive arrangement is not disclosed.
U.S. Pat. No. 3,921,938 describes a helicopter which rotor blades are foldable and which tail is pivotally attached to the fuselage to attain a stowed position of the helicopter.
GB 2,449,743 describes an aircraft which can be dismounted into different parts; inter alia its rear part is entirely separable from the front part of the aircraft.
U.S. Pat. No. 6,050,521 discloses a releasable coupling for a power transmission to a tail rotor of a foldable-tail-section helicopter. The coupling consists of two coupling assemblies, one associated with the front section of the helicopter, the other one associated with the tail section of the helicopter. The two coupling assemblies are coupled via radial toothings, cooperating telescopically with each other.
In view of the above referenced state of the art, it is an object of the present invention to provide a UAV helicopter that has a light-weight, yet robust construction. Furthermore, the power transmission from the engine to the tail rotor is to be efficient and should allow quick and easy connection of the tail section to the fuselage. Additionally, it is an objective to provide for a low noise and easy-to-maintain tail rotor propulsion.